The science of fire
By Fire Fighting in Canada
By Fire Fighting in Canada
The rate at which firefighters are being killed (per fire) in North America as a result of structural collapse and rapid-fire progress has risen steadily over the last few decades.
The rate at which firefighters are being killed (per fire) in North America as a result of structural collapse and rapid-fire progress has risen steadily over the last few decades. This disturbing trend should inspire us to not only understand the factors that have caused this increase, but also to endeavour to correct it.
|Research such as that conducted by NIST and other agencies on the flashover time for legacy and modern spaces is helping firefighters better understand the higher risks associated with today’s fires.
The first step in understanding how to affect this change is to recognize that the working environment for firefighters is dramatically different than it was years ago. As firefighters know, and as Chicago District Chief Peter Van Dorpe told the United States Senate appropriations committee in July during a hearing on the effectiveness of furniture flammability standards and flame-retardant chemicals, “We are making homes larger, building them with fewer [structural] components, and then filling them with more air and more fuel than ever before. From a firefighter’s perspective, this is a recipe for disaster for both the fire service and the public we have sworn to serve and protect.”
Van Dorpe pointed out the need for change. “We need to understand all these things coming together, and how that’s impacting the fire fight and what we need to do differently.”
Fortunately, the North American fire service has an abundance of resources that are helping us understand our increasingly dangerous working environment and, presumably, leading us toward improved operational safety.
Organizations such as the National Research Council of Canada (NRC), the National Institute of Standards and Technology (NIST) and Underwriters Laborites (UL) have been preforming incredibly valuable fire service-related research over the last 10 years or more.
“We’re not doing research for the fire department; we’re doing research with the fire department,” says Dan Madryzkowski, lead fire research engineer of the firefighting technical group at NIST.
This philosophy of developing working partnerships among fire researchers and North American fire services is widely shared among NIST, the NRC and UL and has been very successful.
Peter McBride, division chief of safety and innovation for Ottawa Fire Services, says there is a lack of so-called fire literacy in the fire service that must be addressed to save firefighter lives.
“There is a growing need to involve other partners to conduct research on critical fire literacy issues that affect firefighters and to broaden the understanding of fire literacy,” McBride said in an interview.
“Fire literacy is a common problem among fire services around the world. Simply put, many of the procedures followed by firefighters are based more on traditional practices than on the actual nature of fire and the evidence gained by scientific research into fire behaviour. While the professionalism, skill and instinct of firefighters are often able to mitigate the risks associated with this situation, there are many cases where training that lacks scientific basis puts firefighters at great risk.”
In one of the first major studies to be recognized by fire departments, NIST, with the assistance of the Fire Department of New York (FDNY) and the Chicago Fire Department, focused on the effect of natural wind and the true danger it poses on the fire ground.
|The National Research Council in Ottawa is working with Ottawa Fire Services and other groups to develop a Canadian firefighting research group.
In December 1998, three FDNY firefighters were killed in the line of duty while performing a search on the tenth floor of a so-called fireproof highrise, with exterior winds of almost 50 kilometres per hour (km/h). Wind effects, while not previously quantitatively studied to this degree, proved to be extremely influential to fire behaviour and presented a great risk to firefighters.
“These experiments demonstrated the extreme thermal conditions that can be generated by a simple room-and-contents fire, and how these conditions can be extended along a flow path within a real structure when wind and an open vent are present,” NIST says in its report, called Firefighting Tactics Under Wind Driven Fire Conditions (http://fire.nist.gov/bfrlpubs/fire09/art015.html ).
This study was conducted in the context of highrise buildings but it holds important messages that all fire departments should examine and the findings are relevant to all structure fires in which wind conditions are present.
Legacy versus modern
With the financial support from a United States Department of Homeland Security firefighter grant program, fire engineers at UL in Northbrook, Ill., have been able to do various groundbreaking studies with the fire service. UL has examined in great detail the effect of fires on engineered lumber, basement fires, numerous ventilation studies, as well as the flammability of modern furniture, and UL videos have been widely used by fire-prevention and public-education officers across Canada and the United States to drive home the point about smoke alarms and escape plans.
In one such experiment, UL demonstrated the true impact modern home furnishings are having on fire behavior, when two identical living rooms were constructed for test burns. The first was furnished only with legacy furnishings, which contained only natural products such as wools and cottons, similar to furnishing that would have been found in homes in the 1970s. The second was furnished with modern furnishings, constructed of mostly synthetic products, similar to most homes found today. The results were both staggering and eye opening. While the legacy room reached flashover in a time of 29:25, the modern room reached flashover in just 3:40.
The most recent project on which UL, NIST and the FDNY collaborated in July, may have the largest impact on the fire service. The project, which challenged many conventional procedures and fire-ground tactics, tested both traditional and non-traditional tactics for six days in acquired structures.
|Firefighters must train in new techniques to adapt to new materials and new environments, says Underwriters Laboratories.
Although the official report has not yet been officially released, early observations by some members of the FDNY are already causing fire officials to re-evaluate the way they have been performing ventilation during fires.
“Fires are consuming all the oxygen in a building and when we ventilate a building we’re causing a ventilation-induced flashover, and that impacts the safety of our firefighter,” says Robert Maynes, deputy assistant chief for the FDNY.
“This is a great opportunity to find out what happens at non-fireproof fires and hopefully save firefighters lives in the future.”
But the critical impact of oxygen on a developing fire is not the only traditional belief that is being shaken by this study. While focusing directly on the application of water from the outside, the long-serving belief held by some departments that this is a dangerous tactic was also confronted, and results were unexpected by many firefighters with the FDNY. Conversely, to fire engineers, the results only went to further confirm their results from previous studies regarding the myth of pushing fire.
“Everyone thought you could never put water into a window from the outside because you’re going to push the fire into the structure,” says Steve Kerber, a fire engineer with UL, who also has 13 years’ experience working as a firefighter and officer.
“We’ve done upwards of 100 tests in different structures, with different-sized fires, with different hose streams, with different lines, with different flows, and we are yet to push fire into a structure. [Conditions] get better every single time. Every time the temperatures in the entire structure go down.”
The National Research Council of Canada (NRC) also has strong history of fire service-related testing and continues today.
In 2002, the NRC explored European techniques of cooling fire gases during interior operations and subsequently released the report, Review of Three Dimensional (3D) Water Fog Techniques for Firefighting.
Similar to NIST and UL with their challenge to some of our historical practices, this report from the NRC found our traditional methods of gas cooling may not be as effective as we thought.
“Compared to traditional straight stream or narrow fog techniques, both experimental and analytical results show that proper use of a 3D water fog technique can have a better cooling effectiveness, generate less steam and lead to less disruption of the thermal balance in the smoke layer by using short discharges, fine droplets and wide spray angle,” the NRC Report went on to state.
“[With the 3D technique,] the smoke temperature was quickly reduced by 200 to 250 C and then continued to cool. With the straight stream tactic, the overhead temperatures were reduced initially but quickly returned to their original level.”
Today, the NRC continues to assist Canadian fire services with research and development. Recently, with the assistance of Ottawa Fire Services, the NRC has been working to develop the Canadian firefighting research group. This new group, which will include fire service members from across the country, will focus on:
- Evaluating new firefighting tactics and equipment during live fire experiments.
- Assessing health hazards posed by new building materials and techniques.
- Developing more realistic firefighting training aids.
With its first inaugural meeting planned for the near future, the new Canadian firefighting research group has the potential to greatly affect the ways in which we go about our daily operational duties.
While fire is a chemical and physical reaction, historically the North American fire service has not used or listened to science. Instead, we tend to rely heavily on tradition and experience, and continue to do things because that’s the way they’ve always been done, but adapting to challenges is critical.
“For a firefighter, it’s extremely important that you continue to innovate your tactics,” says Steve Kerber of Underwriters Laboratories.
“If you keep using old tactics for a new fire environment, then it’s probably not the most effective thing to do.”